It is well known to produce percarboxylic acids by reaction of hydrogen peroxide with water miscible carboxylic acids. This reaction takes place in the presence of a catalyst and the water introduced with the hydrogen peroxide, and the water formed during the reaction is continuously removed by azeotropic distillation by means of an organic solvent capable of forming a hetero-azeotrope.
The reaction of hydrogen peroxide with carboxylic acids is the equilibrium reaction: ##STR1##
This reaction should also generally occur at reduced temperatures because of the instability of the percarboxylic acids formed. To accelerate the reaction, catalysts are used which most frequently are strong organic or mineral acids, such as phosphoric acid, sulfuric acid, hydrochloric acid, alkyl or aryl sulfonic acids, trifluoroacetic acid, or acid cationic resins.
To displace the equilibrium of the reaction (I) toward the right, it has been proposed to continuously remove the water by azeotropic distillation (see U.S. Pat. Nos. 2,877,266 and 2,814,641, for example). It is also known that the strong acid catalysts can be advantageously replaced by a boric acid (U.S. Pat. No. 4,338,260) or a metalloid oxide (U.S. Pat. No. 4,330,485).
These processes for preparing percarboxylic acids using hetero-azeotropic distillation of the water during the reaction, however, have a number of significant disadvantages. For example, a significant quantity of the hydrogen peroxide is removed by the azeotropic distillation and ends up in the distilled aqueous phase. Also, the entrained peroxidic oxygen is in the form of untransformed hydrogen peroxide and/or percarboxylic acid. This peroxidic oxygen entrained in the distilled aqueous phase is present regardless of the catalyst used. These losses can reach up to 4% of the hydrogen peroxide initially used in the reaction, as shown by B. Philips et al., in the JOURNAL OF ORGANIC CHEMISTRY, 23, 1823 (1958) and M. Hrusovsky, in CHEMICAL ABSTRACTS, 78, 123937.
In addition to these losses in the distilled aqueous phase by entrainment during the azeotropic distillation, there are also appreciable losses of hydrogen peroxide by decomposition in the azeotropic distillation column. The hydrogen peroxide carried away with the organic-water hetero-azeotrope are subjected to conditions in the distillation column that promote or cause its decomposition. This decomposition of the hydrogen peroxide in the column is accentuated since it no longer contains the stabilizer initially introduced into the reaction mixture by way of the hydrogen peroxide aqueous solution.
The peroxidic oxygen losses due to entrainment and decomposition of the hydrogen peroxide in the azeotropic distillation column make this process of preparing percarboxylic acids economically burdensome.
In all of these prior art processes, the reactor containing the hydrogen peroxide, water, carboxylic acid, the catalyst and the organic solvent acting as the azeotrope entraining agent is below the distillation column which is equipped with a condenser and a decanter. The organic phase is refluxed back into the distillation column after being decanted from the aqueous phase while the decanter aqueous phase is drawn off continuously and discarded.